A conventional flexible bearing may comprise a lamination of alternating layers of an elastomeric material and rigid reinforcement shims that are stacked and bonded together. Both the top and bottom layers may be an elastomer, and the lamination is positioned between and bonded to metallic end rings. One end ring may comprise the thrust-nozzle ring of a rocket motor, and the other may comprise the rocket case mounting ring. The lamination may be laterally flexible, that is, in directions parallel to the layers, but unyielding in the directions perpendicular to the layers.
A flexible bearing used in a rocket motor application is exposed to excessive heat and/or flame. The rigid reinforcement shims of the bearing may be metal, and may withstand the heat. However, the elastomer layers may deteriorate, beginning with the peripheral portions which are exposed to the heat or flame. The deterioration adversely affects the incompressibility of the laminated stack and the ability of the stack to accommodate torsional rotation.
One solution to the need for thermal protection of a flexible bearing is disclosed in U.S. Pat. No. 3,519,260 to Irwin. The laminated bearing stack is alternate layers of elastomer and bearing material, and the peripheries of the bearing material extend beyond the peripheries of the elastomer layers. The extension of the bearing material layers beyond the elastomer layers provides flame traps between the bearing material layers. In addition, the extension of the bearing material layers provides heat radiating vanes along the periphery of the flexible bearing.
A drawback to the extended bearing material design for a flexible bearing is that any damage to extended bearing material layers requires the entire flexible bearing to be replaced. The flexible bearing is an expensive component; therefore, frequent replacement is not desirable.
Another thermal protection device for a flexible bearing is disclosed in U.S. Pat. No. 4,263,243 to Wilson, the disclosure of which is incorporated herein by this reference. The protective heat and flame barrier is formed by providing an especially refractory outer edge on each shim, which extends beyond the layers of elastomer. The protective edge is formed on each shim by attaching an edging of resin-filled cloth, of especially refractory properties, to the outer edge of at least some of the segments before arranging them in a mold.
Any damage to the protective edge of the Wilson thermal protection device will result in a reduction in thermal protection, or the entire bearing must be replaced. In addition, the bearing having protective edges acts as a pressure barrier, trapping heated gases between the protective edges and the elastomer layers.
Therefore, there is a need for a thermal protection system for a flexible bearing which is replaceable, flexible, and does not act as a pressure barrier.